In the design and development of new plastic containers, there is often a need to produce a prototype of a part intended eventually to be mass produced by blow-molding. Containers of this type are constructed by placing a parison between two halves of a blow-mold, closing the mold, and then blowing the parison against the inside wall surface of the mold. The molds typically used in blow-molding machines for production purposes are machined from durable and long-lasting tool steel alloys, and this is a slow and expensive procedure if it is intended to produce only a few parts to test a design. For example, it is often desired to construct prototype containers for showing to customers, or for providing a limited run of containers. Although conventional prototype tooling and methods of constructing the same are much less expensive, and require less time for construction and delivery, than production tooling, nevertheless such prototype tooling still is fairly expensive and requires typically several weeks for construction and delivery.
In one type of blow-molding machine, referred to as a shuttle blow-molding machine, whether single stage or two stage (with both pre-form and final blow-mold halves), each mold half is carried on an associated platen displaceable along tie bars by a power means such as a piston and hydraulic cylinder. Examples of such shuttle type blow-molding machines are shown in U.S. Pat. Nos. 3,767,747; 3,781,395; 3,978,184; 4,070,428; and 4,118,452. The mold halves even when constructed for prototype molding purposes are typically relatively massive and complex structures fastened only at their back faces to the platen for a cantilever type mounting thereon. The mold halves themselves are built to withstand both the compressive and tensile stresses exerted during the molding operation both in the direction of mold travel as well as laterally in directions parallel to the closing plane of the mold halves. In addition, it is necessary to provide liquid cooling for each mold half and thus involves machining interior cooling channels and passageways for the cooling fluid in each mold half. Alignment pins and bushings as well as vent deflectors, are typically also built into the mold halves.
As pointed out in U.S. Pat. Nos. 5,458,825 and 5,641,448 (incorporated herein by reference), in recent years, one method for making prototype parts cheaply and quickly has been to first produce a geometric computer model of the part using computer aided design (CAD) to create a geometric computer model. A suitable CAD tool is that known as "PRO/ENGINEER". This model is then used as input to another software package called "PRO/MOLD" where the core and cavity portions of the mold are designed, and adjusted for shrink allowances of a plastic molding process. Both of these software packages are available from Parametric Technology Corporation of Waltham, Mass. USA. This produces computer models of the mold portion or portions. As set forth in the '488 patent, this computer model then may be used as the control input in a stereolithographic apparatus (SLA) as a form of solid free form fabrication. Alternatively, as pointed out in the '825 patent, the CAD model can be used to generate the control signals for computer and numerical control (CNC) paths for a cutting tool of a CNC three axis machining set up to determine the paths for the cutting tool to follow in cutting an actual single cavity prototype mold from aluminum or other metal. However, this still can be costly and time consuming if the prototype mold is designed and constructed along conventional lines for typical mold halves as mounted in a typical blow molding machine, and production conditions also are to be simulated as closely as possible to verify suitability of the prototype container design so molded.
On the other hand, if in order to save time and money for prototyping a photo-sensitive polymer or resin is to be used as the material to make the mold instead of making the mold out of metal, fewer parts can be molded and with less accuracy than a mold made of metal such as alloys of aluminum, steel, beryllium copper that are typically used for production plastic molding.